Structure and method for separating insoluble particles from a molten bath

ABSTRACT

A device and method particularly suitable for separating particulate matter in a molten salt or molten metal bath from the bath. The device comprises a unitary bowl and pump structure adapted to be immersed into and rotated in a pool of the bath, and to draw into the bowl the bath and particulate matter when the bowl is rotated. With rotation of the bowl, the particulate matter, in large measure, is collected in a concentrated form in the bowl while the bath, which is now largely depleted of particulate matter, is discharged from the bowl. To remove the particulate matter, and any bath entrapped therewith, from the bowl, the bowl is removed from the bath and a blade means is inserted into the bowl to scrape the particulate matter from the bowl. The particulate matter falls from the bowl through an opening provided in the lower end thereof. After the particulate matter is removed from the bowl, the bowl is returned to the bath for another cycle of collection and particle removal.

United States Patent [191' Racunas et al. Apr. 2, 1974 [54] STRUCTUREAND METHOD FOR 371,755 4/1932 Great Britain 233/17 SEPARATING INSOLUBLEPARTICLES 3 3 32 3? a 233/46 FROM A MOLTEN BATH 0/ 4 ermany 233/28 [75]Inventors: Bernard J. Racunas, New I Kensingmn. John Minick UpperPrimary Examiner-George H. Krizmamch Burren Twsp both of Pa. Attorney,Agent, or Firm-Elroy Strickland [73] Assignee: Aluminum Company ofAmerica,

Pittsburgh, Pa. 57 ABSTRACT [22] Filed: Sept 1972 A device and methodparticularly suitable for separat- [21] Appl. No.: 293,017 ingparticulate matter in a molten salt or molten metal bath from the bath.The device comprises a unitary bowl and pump structure adapted to beimmersed into [22] 2334336413215; and rotated in a pool of the bath, andto draw into the 46 28 3 bowl the bath and particulate matter when thebowl is 1 1e 2 8 7 1 668; rotated. With rotation of the bowl, theparticulate matter, in large measure, is collected in a concentratedform in the bowl while the bath, which is now largely depleted ofparticulate matter, is discharged, [56] References Cited from the bowl.To remove the particulate matter, and UNITED STATES PATENTS any bathentrapped therewith, from the bowl, the bowl 1,056,233 3/1913- Trent233/3 is removed from the bath and a blade means is in- 980,001 12/l910Ponten 233/3 Serted i t the bowl to scrape the particulate matter313091015 3/1967 Jung at 233/10 from the bowl. The particulate matterfalls from the 2 7/1914 Lougher 53 bowl through an opening provided inthe lower end thereof. After the particulate matter is removed from2,447,330 8/1948 Grcbmcier 233/26 the how], the h returhed the bath foranother cycle of collectlon and partlcle removal. FOREIGN PATENTS ORAPPLICATIONS 362,652 7/1962 Switzerland 233/3 10 Claims, 3 DrawingFigures PATENTEU APR 2 I974 FIG.

FIG. 3.

STRUCTURE AND METHOD FOR S EPARATING INSOLUBLE PARTICLES FROM A MOLTENBATH BACKGROUND OF THE INVENTION The present invention relates generallyto liquidsolids separation, and particularly to a structure and methodcapable of rapidly and economically separating non-metallic solids andparticles, substantially insoluble in a molten salt and/or metal bath,from the bath.

There has been considerable interest over the years in the subject ofseparating particulate solids contained in molten baths of metal andsalt from the baths, which interest has generated a substantial amountof literature describing different structures and procedures attemptingto accomplish such separation in an economical manner.

It has long been known that molten salt fluxes are effective inseparating aluminum from non-metallic impurities, such as oxide, carbideand nitride solids of the aluminum, in such scrap forms as skim, dross,powder,

turnings and other forms of scrap. The utilization of the separatingconcept, however, has been hampered by the lack of means that areefficient and rapid in removing the solids, which accumulate as a resultof the separating process, from the molten salt once separation of thenon-metallic impurities and metal has occurred.

Rotary salt furnaces, for example, are effective in separating oxidesand other non-metallic solids and impurities from aluminum but at theend of the separating process, a considerable amount of salt is dumpedfrom the furnace with the accumulated non-metallic impurities. The saltand impurities must then be further processed to separate the salt fromthe impurities so that the salt can be reused in the rotary furnace.This further processing of the salt and impurities adds costs to themetal-solids separating process, which costs could be elminated or atleast substantially reduced if means were available for rapidly andeconomically removing the solids from the salt bath.

Another area of interest involving liquid-solids separation, in which itis advantageous to effect such separation in a rapid and economicalmanner, is the making of magnesium from magnesium chloride. Here itwould be advantageous if insoluble impurities were separated from themagnesium chloride before it is used in an electrolytic reduction cell.

Thus, in the area of metal reclamation, as well as in other areasinvolving molten baths containing solid materials of low solubility inthe bath, it is desirable that a liquid-solids separation device andprocess be found that provides salt economy and high metal recovery, andthat lends itself to being automated for further economy and efficiency.

BRIEF SUMMARY OF THE INVENTION The present invention provides such adevice in the form of a simple, unitary bowl and pump means adapted tobe immersed into and rotated in a pool of a molten liquid bath of metalor salt containing solid impurities. With rotation of the bowl in thepool, the bath and solids are directed to the side of the bowl bycentrifugal force while the pumping means directs the liquid salt ormetal, now substantially depleted of the solids, from the bowl and intopool in which the bowl is immersed. The solids are trapped inside thebowl adjacent the side wall thereof, and are removed from the bowl by ascraping means inserted therein when the bowl is removed from the bathand pool. After the solids are removed from the bowl, the scraping meansis withdrawn and the bowl returned to the bath for a repetition of theabove process.

The bowl and pump means, as briefly described thus far, provides a metaland salt economy, heretofore unavailable, by concentrating solids in thebowl to such a high degree that minimum metal and salt liquid areentrapped with the solids, and thus minimum metal and salt is removedwith the solids when they are scraped from the bowl. With presentlyavailable liquid-solids separation processes, such entrapped metal andsalt is of a substantially greater quantity, and it is lost when and ifthe solids are discarded.

The device and operation of the present invention readily lends itselfto being automated so that the liquid-solids separating and removalfunctions of the invention are both-rapid and essentially continuous. Further, since the liquid salt is returned to the pool, in molten saltapplications, and only the solid particles are removed from the bath,with a minimum amount of salt collected with the particles, the salteconomy of the present invention is considerably improved over priorprocesses which dispose of the salt and insolubles together.

THE DRAWING The invention, along with its objectives and advantages,will be more apparent after consideration of the following detaileddescription in connection with the accompanying drawing in which:

FIG. 1 shows a vertical section of the unitary bowl and pump of thepresent invention;

FIG. 2 is a side elevation view of a blade for scraping insolublematerial from the bowl of FIG. 1; and

FIG. 3 is a perspective view ofa plate structure forming the lower endof the bowl of FIG. 1.

PREFERRED EMBODIMENTS OF THE INVENTION Referring now to the drawing,FIG. 1 shows, in vertical section, a unitary bowl and pump structure anddevice generally designated 10. The bowl is shown comprised of agenerally cylindrical side wall 12, though the invention is not limitedthereto, and opposed, top and bottom end walls 14 and 16. The end wall14, as shown in FIG. 1, may be provided with an opening 18 toaccommodate a pump impeller 20. The impeller is attached to orintegrally formed with the bowl to rotate therewith as explained ingreater detail hereinafter. Peripheral openings 22 are provided in awall of a hub portion 24 above the impeller, the external surface of thehub portion, in turn, being provided with vertically extending,peripheral vanes 26. A center recess 28 ex tends into the hub portionfrom the top thereof, and is dimensioned to receive a shaft 30 forrotating the bowl and pump device 10.

As shown in FIG. 1, the shaft 30 preferably comprises an inner, solidshaft structure 32 made of high strength metal surrounded by a corrosiveresistant sleeve 34 made of material such as graphite. The recess 28receiving the shaft 30, and the portion of the shaft extending into therecess may be provided with mating planar surfaces to effect rotation ofthe bowl and pump mechanically coupled thereto.

The end wall 16 at the bottom of bowl preferably comprises a platestructure (FIG. 3) provided with a center opening 36 and a plurality ofslanted openings 38 (FIG. 1) located about the center opening. On thesurface of the plate facing downwardly and outwardly from the bowl arelocated pumping blocks 40, the slanted openings 38 extending through theplate and preferably through the blocks in the manner shown in FIG. 1,which blocks may be formed integrally with the plate.

With the use ofa plate such as 16, the inner diameter of the bowl at itslower end is widened somewhat to provide a downwardly facing annularledge 42, below which is a threaded portion 44. The plate 16 is securedin the bottom end of the bowl and in abutting engagement with the ledge42 by a ring 46 having its outer edge provided with threads, the ringbeing threaded into the threaded portion 44 of the bowl as shown inFIG. 1. The plate may be suitably keyed to the side wall of the bowl toprevent its rotation relative to the bowl.

In a similar manner, the impeller 20, if used and if it is a separatestructure, must be suitably fastened to the bowl so that it rotates withthe bowl when the bowl is rotated. In the operation of bowl 10, the bowlis rotated about its axis, and the impeller 20, with the pumping blocks40 and the'vanes 26, function as pumping means to direct a molten bathinto and out of the bowl in a manner presently to be explained. Sincethe impeller, vanes and blocks are effective as pumping means, it is notnecessary, for the purposes of the invention, to employ all three means,

Since the bowl and pumping device operates immersed in a pool of moltenbath (not shown) and in corrosive environments, the material of the bowland pumping means must be heat and corrosion resistant. To this end,graphite has been found to be a suitable material for the device 10. Inaddition, a graphite bowl with an end plate 16 made of silicon carbide(for abrasion resistance) has operated successfully in molten salt andcombinations of molten salt and molten aluminum baths. The structure ofthe invention, however, is not limited to graphite and silicon carbidematerials, nor is it limited to a separate bowl and plate construction.

The bowl and pump structures may be cast as a single unit, though thepreferred embodiment of the invention is to provide a separately madeend plate 16, as discussed above and as shown in the figures, and aseparate impeller 20, if used. The end plate may be cast to provide thepumping blocks 40 integral therewith, and the slanting holes 38 can beprovided in the casting process, or drilled through the blocks andplate.

In the operation of the bowl and pump device 10, the device is immersedin a pool of a molten salt or metal contained within a furnace, forexample, the salt or metal containing solid or particulate impuritiesthat have a specific gravity generally greater than that of the salt ormetal, and that need to be removed therefrom for anyone of a number ofreasons and purposes, such as those outlined earlier in discussing thebackground of the invention. The bowl, with its associated pumpingimpeller 20, blocks 40 and/or vanes 26 is rotated in the bath at asuitable speed by the shaft 30, which may, in turn, be rotated by asuitable motor (not shown) mechanically connected thereto. With rotationof the device, the vanes and the impeller or blocks (or all three) areeffective to direct into the bowl the molten salt,

molten metal and solid particles through the opening 36 and throughopenings 38 provided in plate 16.

As the particles enter the rotating bowl, they are directed to the sidewall thereof by centrifugal force acting upon their heavier mass and bythe impetus given to them by the slanting holes in the bottom plate. Asthe particles reach the walls of the bowl they tend to concentrate andcollect thereon while the molten salt or metal is directed from the bowlthrough the openings 18 and 22 in the upper wall 14 of the bowl. In thismanner, the salt or metal pumped into the bowl is returned to the poolin a state substantially depleted of particulate material.

The rotation of the bowl is continued until a sufficient amount ofparticles or concentrate is collected in the bowl along its side wall,as indicated by numeral 48 in FIG. 1. The bowl is then raised above thelevel of the pool for the insertion of a means to scrape the particlesfrom the bowl in a manner presently to be explained.

The particles and solids concentrated and collected in the bowl, can beremoved therefrom by a simple blade structure 50, as shown in FIG. 2,mounted in an upright position. The width and height of the blade aresuch that the blade can be inserted into the bowl through the opening 36in the bottom wall thereof, and be moved laterally within the bowl andinto the concentrate 48 collected therein. With the blade so positioned,the bowl is rotated about its axis, the concentrate moving past theblade to be scraped from the bowl. As the concentrate is scaped from thebowl, it falls through the opening 36, and may be collected in asuitable container-or pan 52 positioned beneath the bowl.

The operation of the structure, as thus far described, is preferablyautomated, which operation may function in the manner presently to bedescribed, keeping in mind that the invention is not limited thereto.

While the bowl and pump 10 is in the molten pool of a salt or metal,from which it is desired to separate solid impurities therefrom, andwhen the bowl and pump is removed from the pool and furnace, with theconcentrate 48 collected in the bowl, the blade 50 is located above thebath or furnace in an out-of-the-way position, i.e., in a positionexternal to the path traversed by the bowl as it is removed from thefurnace. The bowl is lifted to a height above the furnace sufficient forthe blade to be moved under the bowl. The raising of the bowl can beinitiated and automated by the use of a timing device, and the moving ofthe blade to a position under the bowl can be automated by limitswitches or other types of proximity devices. For example, when the bowlreaches a height above the furnace to accommodate the blade thereunder,a limit switch can be actuated to cause energization of an actuatingmeans capable of bringing the blade into position under the bowl. In asimilar manner, when the blade is positioned and centered beneath theopening 36 in the bowl end wall 16, the bowl is lowered over the bladeto a position where the end wall 16 of the bowl is clear of the loweredge of the blade. Similarly, the motor for rotating the bowl shaft 30is then energized, and the blade is actuated to move laterally into theconcentrate 48 within the bowl. With the blade engaging the concentrate,and with the bowl rotating, the concentrate is scraped from the bowl aslateral movement of the blade into the concentrate continues.

To collect the concentrate scraped from the bowl in the pan 52, the pancan be positioned under the bowl automatically in a manner similar tothat described above in connection with the automated movement of thebowl and blade.

After a time period sufficient to scrape essentially all of the solids48 from the bowl, the rotation of the bowl is stopped, preferablyautomatically, and the reverse of the above sequence takes place. Thebowl is thus raised above the blade, and the blade is moved to one sideof the bowl. The bowl is then vertically lowered into the molten bath tocollect solids therein (again) in the manner described above.

Whether the structure and process of the invention is automated oroperated under manual control of personnel, the structure and processprovides a rapid and essentially continuous process for collecting andseparating particulate impurities from a molten salt or metal bath. Inaddition, the process of disposing and rotating the bowl in a pool ofthe molten bath, as well as the process of removing the bowl from thebath and pool, and inserting and removing the scraping device 50 fromthe bowl, involve rather straight forward mechanical movements. Thisallows the structure of the invention to be mounted and moved withoutsubstantial difficulty, equipment and cost so that the present inventionprovides the essentially continuous and rapid process for removingimpurities in an economical manner.

While the invention has been described in terms of preferredembodiments, the claims appended hereto are intended to encompass allembodiments which fall within the spirit of the invention.

Having thus described our invention and certain embodiments thereof, weclaim:

1. A device for removing particles from a bath of molten salt or metal,or from a bath comprised of molten salt and metal, said devicecomprising a unitary bowl and pump means made ofa heat and corrosiveresistant material and adapted to be rotated about a common axis, and tobe immersed in and removed from a pool of the molten bath,

said bowl having opposed end walls, with entrance and exit openingsprovided in said walls for respectively admitting and discharging thebath to and from the bowl,

said pump means including pumping blocks located on the outside surfaceof the end wall having the entrance openings, and

shaft means for rotating said bowl and pump means,

said pump means being effective, when rotated in said bath, to directthe bath through the bowl while said bowl is effective to concentrateand collect the particles in' the bowl adjacent the sides thereof.

2. The structure of claim 1 in which the entrance openings comprise acenter opening and a plurality of openings spaced about the centeropening.

3. The structure of claim 2 in which the plurality of entrance openingsextend diagonally through the end wall and through the pumping blocks.

4. The structure of claim 1 in which the pump means includes an impellerlocated adjacent the exit openings.

5. The structure of claim 1 in which the bowl is provided with externalvanes located adjacent the discharge openings.

6. The structure of claim 1 in which a separate, abrasive resistantplate structure forms an end wall of the bowl.

7. The structure of claim 6 in which the separate plate structure issecured in one end of the bowl by a ring means threaded into said end.

8. A method of removing suspended particles from a pool of a moltenliquid salt or metal bath, or a bath comprising both molten salt andmetal, the method comprising the steps of immersing a bowl having a sidewall and unitary pump means in said pool,

rotating said bowl and pump means about a common axis within said poolto draw the bath and particles into the bowl through an entrance openingtherein, the centrifugal forces produced by the rotating bowl beingeffective to direct the particles toward 7 the side wall of the bowl forcollection thereon while the bath is directed therefrom through an exitopening,

periodically removing said bowl, with the particles collected therein,from said pool, and

removing the particles from said bowl.

9. The method of claim 8 wherein the collected particles are removedfrom the bowl by inserting a scraping device into the bowl through theentrance opening therein,

moving said device into engagement with the particles, and

moving the bowl or scraping device relative to the other about the axisof the bowl to scrape the particles from the side of the bowl.

10. The method of claim 8 wherein the bowl is disposed vertically in thepool of the molten bath, and the rotation of the bowl is about itsvertical axis.

1. A device for removing particles from a bath of molten salt or metal,or from a bath comprised of molten salt and metal, said devicecomprising a unitary bowl and pump means made of a heat and corrosiveresistant material and adapted to be rotated about a common axis, and tobe immersed in and removed from a pool of the molten bath, said bowlhaving opposed end walls, with entrance and exit openings provided insaid walls for respectively admitting and discharging the bath to andfrom the bowl, said pump means including pumping blocks located on theoutside surface of the end wall having the entrance openings, and shaftmeans for rotating said bowl and pump means, said pump means beingeffective, when rotated in said bath, to direct the bath through thebowl while said bowl is effective to concentrate and collect theparticles in the bowl adjacent the sides thereof.
 2. The structure ofclaim 1 in which the entrance openings comprise a center opening and aplurality of openings spaced about the center opening.
 3. The structureof claim 2 in which the plurality of entrance openings extend diagonallythrough the end wall and through the pumping blocks.
 4. The structure ofclaim 1 in which the pump means includes an impeller located adjacentthe exit openings.
 5. The structure of claim 1 in which the bowl isprovided with external vanes located adjacent the discharge openings. 6.The structure of claim 1 in which a separate, abrasive resistant platestructure forms an end wall of the bowl.
 7. The structure of claim 6 inwhich the separate plate structure is secured in one end of the bowl bya ring means threaded into said end.
 8. A method of removing suspendedparticles from a pool of a molten liquid salt or metal bath, or a bathcomprising both molten salt and metal, the method comprising the stepsof immersing a bowl having a side wall and unitary pump means in saidpool, rotating said bowl and pump means about a common axis within saidpool to draw the bath and particles into the bowl through an entranceopening therein, the centrifugal forces produced by the rotating bowlbeing effective to direct the particles toward the side wall of the bowlfor collection thereon while the bath is directed therefrom through anexit opening, periodically removing said bowl, with the particlescollected therein, from said pool, and removing the particles from saidbowl.
 9. The method of claim 8 wherein the collected particles areremoved from the bowl by inserting a scraping device into the bowlthrough the entrance opening therein, moving said device into engagementwith the particles, and moving the bowl or scraping device relative tothe other about the axis of the bowl to scrape the particles from theside of the bowl.
 10. The method of claim 8 wherein the bowl is disposedvertically in the pool of the molten bath, and the rotation of the bowlis about its vertical axis.